Effects of pressure variation at each of three baroreceptor sets (carotid sinus, aortic arch, and cardiopulmonary)on heart rate are well documented. Quantitative aspects of their composite effects are still incompletely understood. We will attempt to characterize this quantitative relationship by modeling this multiple pressure receptor-heart rate reflex system. The baroreceptors will be perturbed by mechanical and pharmacological means and the reflex heart rate responses will be evaluated.